The present invention relates to a multi-wire wiper contact for use in a potentiometer or other electromechanical device and, more particularly, to a method of wrapping conductive and nonconductive wire upon a mandrel to form a set of wires helically wrapped into a coil prior to masking and plating the coil to form a subassembly that, after plating, may be continuously unwound from the mandrel as a flat strand which can be subsequently formed into multi-wire wiper contacts.
It is known in the prior art to provide a potentiometer with a wiping arm having multiple spring contact fingers which slidably engage the resistive element thereof. An example of such a multiple wire contact is shown in U.S. Pat. No. 2,760,063 by R. C. Raymer in which noble metal wire is wound upon a carbon rod prior to plating the entire wire coil with copper. A portion of the plated wire coil is then masked with an acid resist and the copper plate is removed from the unmasked areas by etching. The exposed portions of the noble metal wire coil, now joined by copper, are then cut and shaped into the desired contact form.
In my U.S. Pat. No. 3,328,707, a second approach is disclosed for forming a multi-wire wiper contact through the utilization of a plurality of wires having a flattened cross section. My patent teaches the idea of attaching the individually flattened wires to a clip by soldering the wires thereto. Contrary to the interpretation of some, the wiper contacts were formed in a continuous chain by folding a stamped piece of sheet metal about a parallel strand of individual wires. The sheet metal piece was first stamped to form a repeat pattern in the configuration of the clamp and then folded over the parallel strands of wire prior to attaching the wire thereto as by welding or solder. The multi-pattern sheet metal and wire was then cut to form the individual multi-wire wiper contact shown in my U.S. Pat. No. 3,328,707.
Since the issuance of my patent, the size of miniature potentiometers has continued to decrease. The potentiometer and multi-wire wiper assembly described in my patent and developed a decade ago are too large and too expensive for many of today's devices. After considering the approach of others, including: those shown in U.S. Pat. No. 3,579,822 by F. J. Dieterich; U.S. Pat. No. 3,704,436 by R. L. Froebe, et al; and U.S. Pat. No. 3,733,573 by F. L. Dieterich, I conceived an improvement over the device disclosed in my earlier patent which provides for a multi-wire wiper contact similar to that shown in the patents referenced above but eliminates procedural steps required in those patents.